Wetlands are defined here as any area of land where the water table is at or near the surface for some defined period of time, leading to unique physiochemical and biological processes and conditions that are characteristic of shallow flooded systems (Mitch and Gosselink, 1993; Oquist et al., 1996). However, it should be noted that many other definitions also are in use, and care is required in comparing wetland areas in different regions of the world (Lugo et al., 1990; Finlayson and van der Valk, 1995; Finlayson and Davidson, 1999).

Wetlands described in this section include those dominated by forested and nonforested vegetation; those on highly organic soils such as peatlands (partially decomposed plant material); and those on mineral soils, as is often typical of riverine systems. Peatlands are peat-accumulating wetlands and usually are divided into bogs and fens, both of which may be forested. Peatlands are found at all latitudes, from the Arctic to the tropics. The growing vegetation layer of bogs is totally dependent on atmospheric inputs for their water and solute supply; consequently, surface peat layers are acidic and poor in nutrients. Fens receive additional water from overland flow and/or groundwater and typically have near-neutral pH and higher nutrient levels.

Wetlands provide many services and goods, many of which are indirect values (e.g., recreation, education, biodiversity, wild food) and are difficult to quantify. Key ecosystem services and goods considered here include biodiversity, carbon sinks, food, and fiber (peat and wood).

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